Mk.5 is a modified H&K MP5, that fires the 9x19mm round. The magazine is an increased 40 rounds, the iron sights have been removed and replaced with newer Red Dot Sights The handguard now has a three way rail system for personal modifications such as; adding a GP-30XC Grenade Launcher, a XM662 Shotgun, various grips, LAM and Lighting fixtures.